1. Field of the Invention
The present invention relates to a transfer ribbon and a method for production of the transfer ribbon, and particularly relates to a transfer ribbon which has a transferable layer (relief layer) with a relief structure such as hologram and/or diffraction grating and is available for transferring the relief layer in a fine pattern by means of a thermal head, and a method of production of such a transfer ribbon.
The present invention also relates to an image expressing medium and a method for production thereof, and particularly relates to an image expressing medium having an image which contains plural dots of the relief layer transferred from the above described transfer ribbon and can exhibit a lame-like glittering effect based on the dots, and a method of production of such an image expressing medium.
2. Description of the Related Art
A transfer ribbon (transfer foil) provided with a transferable layer having relief structures such as holograms or diffraction gratings can print and express specially decorated images or three-dimensional images, and it can also produce a printed product hard to be forged or duplicated because the hologram and the diffraction grating require high technology for producing themselves and they are therefore difficult to be produced.
For example, the transfer ribbons are available for making cards such as credit card, ID card, prepaid card or the like from the viewpoint of preventing forgery or duplicate, and further available for making ticket- or bill-like papers such as gift certificate, check, commercial paper, bond paper, stock certificate, admission ticket or some other certificates particularly from the viewpoint of impossibility in reproducing of the hologram and the diffraction grating with the use of a multicolor-copying machine. Moreover, because of the visually special effects of the relief, other applications include packaging materials, books, notes, brochures, pamphlets, POPs (point of purchase) or the like.
A method for transferring or printing a relief layer by use of a transfer ribbon is well known as a way to add or fix the relief structures such as holograms or diffraction gratings on articles. In general, the transfer ribbon is composed of at least a substrate and respective layers of a peelable layer, a relief layer having patterns such as holograms and diffraction gratings, a reflection layer and an adhesive layer, which are successively laminated in this order on a substrate. Common methods for transferring or printing by the transfer ribbon include a hot stamping method (also called “ribbon pressing” or “foil pressing”) or a thermal transfer method by a heating roller. In the hot stamping method or the thermal transfer method using the heating roller, the transfer ribbon is positioned between a heated metal stamp or roller and a transfer-receiving material, and the transfer ribbon is pressed on the transfer-receiving material with the stamp or the roller, and then substrate of the ribbon is peeled off. However, the hot stamping method and the thermal transfer method using the heating roller cause a problem of difficulty in precise transfer of fine patterns such as dots having minute areas smaller than several millimeter square (mm2) or dots being present close to each other. A method to form such fine patterns includes an etching method, but it requires many processes so that it takes longer time and much cost.
Recently, a thermal printer equipped with a thermal head capable of easily expressing, through a transferring process, dots with minute areas or dots being present close to each other has been commercially available, and a heat melting type or dye-sublimating type ink ribbon is used therein.
The Japanese patent application Laid open (JP-A) No. Heisei 11(1998)-227368 discloses a method to transfer dot patterns by means of a thermal head. Applicable range of this invention is however restricted to the case of forming dots lager than a certain area, and this fact suggests presence of considerable difficulty in expression of fine patterns. Moreover, conventional transfer ribbons have low sensitivity toward instantaneous heating by a thermal head, so that they provide very low printing speed and further provide faults of causing lacks or chipping of the dots to be transferred on a transfer-receiving material or causing burrs, that is, layers being transferred and left in areas between the dots on the transfer-receiving material. The above mentioned JP-A No. Heisei 11(1998)-227368 teaches or suggests no method to solve these problems for improvement of the transfer ribbons.
The Japanese patent application Laid open (JP-A) No. 2001-315472 discloses a method to make glittering image by transferring relief layers in multiplies form with the use of several transfer ribbons with different diffraction directions each other. However, the above mentioned method requires a number of transfer ribbons and multiple transfer processes. In addition, a conventional transfer ribbon is involved with a fault of considerable difficulty in transferring fine dots without causing burrs and lacks of dots.